Abstract
We present dynamical measurements from the KMOS (K-band Multi-Object
Spectrograph) Deep Survey (KDS), which is comprised of 77 typical star-forming
galaxies at z $\simeq$ 3.5 in the mass range 9.0 < log(M$_\star$/M$_ødot$)
< 10.5. These measurements constrain the internal dynamics, the intrinsic
velocity dispersions (\sigma$_int$) and rotation velocities (V$_C$) of
galaxies in the high redshift Universe. The mean velocity dispersion of the
galaxies in our sample is \sigma$_int$ = $70.8^+3.3_-3.1$ km s$^-1$,
revealing that the increasing average \sigma$_int$ with increasing
redshift, reported for z $łesssim2$, continues out to z $\simeq$ 3.5. Only 34
$\pm$ 8% of our galaxies are rotation-dominated (V$_C$/\sigma$_int$ > 1),
with the sample average V$_C$/\sigma$_int$ value much smaller than at
lower redshift. After carefully selecting comparable star-forming samples at
multiple epochs, we find that the rotation-dominated fraction evolves with
redshift with a z$^-0.2$ dependence. The rotation-dominated KDS galaxies show
no clear offset from the local rotation velocity-stellar mass (i.e.
V$_C$-M$_\star$) relation, although a smaller fraction of the galaxies are
on the relation due to the increase in the dispersion-dominated fraction. These
observations are consistent with a simple equilibrium model picture, in which
random motions are boosted in high redshift galaxies by a combination of the
increasing gas fractions, accretion efficiency, specific star-formation rate
and stellar feedback and which may provide significant pressure support against
gravity on the galactic disk scale.
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